# Using an Induction Heater to melt multiple types of metal

Right, here's some context. I have a large amount of metal shavings from a dozen different sources, and they are very light and sharp. Some of them aren't, but most of them are. I need to dispose of them without ruining the day of an unlucky employee at a recycling plant. So I intend to melt them into easily organized and transportable ingots.

The only problem is, I also want to learn how to make an induction heater, and all of those metal shavings sound like perfect test subject for this project.

Now, when it comes to making an induction heater, my research has informed me that I need a Tank Capacitor hooked up to an oscillating power supply. The Tank Capacitor part sounds simple enough, I have serviceable capacitors for days, and I have copper pipe from a plumbing project that went nowhere, for the work coil.

The project got complicated when the concept of resonance got introduced. A quick wiki-crawl and an examination of several similar projects revealed that a Tank Capacitor has a specific resonance frequency, where the energy gain (Transfer? Whatever.) is at it's most efficient. The equation can be found with a quick google. However, the inductance, one of the variables used to determine the resonance frequency, changes based on the contents of the work coil. I have been led to believe that it also changes based on how hot the work piece is.

So I have to ask, how do I determine the resonant frequency while the work coil is functioning? Can I just attach a wire to the Tank Capacitor to determine the frequency that its oscillating at, and get the resonant frequency from that?

• employees at a recycling plant already expect everything to be sharp. i do not think that you will surprise them. Mar 16, 2018 at 22:46
• It's less about cutting someone, and more about being impossible to organize if they cut their way out of the bags. Mar 16, 2018 at 22:58
• The inductance & capacitance together form a resonant 'tank circuit'. A 'Tank Capacitor' isn't really a thing, and doesn't really have a resonant frequency of its own (at least not one relevant to what you're trying to do). Mar 17, 2018 at 2:28
• You can just assemble your work coil and capacitor, and stimulate them with a step function, then see what frequency they resonate at. The easiest way to do the step function would be to connect a small battery (like a 9V transistor battery), then remove it and watch the sine wave with an oscilloscope. You can do this with and without metal in the coil. You are not going to be actually heating up the work piece. Just observing the frequency. It doesn't matter that it is a low voltage. Mar 17, 2018 at 4:27
• Having large unknown alloy chunks will ruin his day more than shavings that he can sort if he wants Mar 17, 2018 at 8:58